1. Field of the Invention
The present invention relates to a circuit for preventing an output of a pop noise occurring from an audio amplifier, and more particularly to a circuit for preventing an output of a pop noise, which occurs from an audio amplifier when a power switch of an electronic device loading the audio amplifier is turned on/off, from being outputted through a speaker connected to the audio amplifier.
2. Description of the Prior Art
In a variety of electronic devices having an audio amplifier, when a power supply of the device is turned on/off, there occurs a noise due to a time interval until the power supply is turned on/off. The noise may instantaneously occur in the audio amplifier due to an unstable ground. Such noise is called a pop noise. The pop noise is outputted through a speaker connected to a rear end of the audio amplifier, so that a user may feel uncomfortable.
In regard to this, an audio output circuit of a general electronic device may comprise an audio amplifier 10, a power supply 11 and a controller 12, as shown in FIG. 1. The audio amplifier 10 receives an audio signal, amplifies the received signal to a predetermined level, and then outputs the amplified signal. The power supply 11 supplies a necessary power to the audio amplifier 10, and the controller 12 outputs a control signal to control on/off states of the power supply 11.
In the conventional electronic device, when a user turns on/off the power supply using a switch (not shown), the controller 12 turns on/off the power supply 11 supplying the power to the audio amplifier 11. When the power supply 11 is turned on/off, there occurs a pop noise in the audio amplifier 10.
Specifically, as the power supply 11 is turned on, an output of the audio amplifier 10 is instantaneously increased to a direct current (DC) voltage (high level) from a ground voltage (low level). On the contrary, when the power supply 11 is turned off, the output of the audio amplifier 10 is instantaneously dropped to the ground voltage (low level) from the DC voltage (high level). As a result, there instantaneously occurs a pop noise in the audio amplifier 10 and the pop noise is outputted through a speaker (SPK). Like this, in the electronic device having the audio amplifier according to the prior art, when the power is on/off, the pop noise is outputted, so that the user feels uncomfortable.